Many unforeseen applications of GPS have been developed in recent years. One such application is passive ranging using the GPS standard positioning system (GPS-SPS). A method to measure the distance between a given target and an observation point without a GPS receiver at the target or knowing the exact location of the target has been developed and tested. No signal is emitted by the user to find the distance to the target. Only the reception of GPS signals is required. This approach conventionally requires two GPS receivers. One receiver uses a conventional GPS antenna to receive the signals directly from the satellites. The second receiver uses a high gain antenna directed at the target and receives GPS signals reflected from it. The direct GPS receiver determines the positions of the satellites so the distance from the satellites to the user can be determined (and the user position if not known). The second receiver is used to process the reflected signals from the target to measure the total distance from the satellite to the target and the target to the user. Target distances of up to 64.9 meters have conventionally been measured with approximately 1-2 meters of error.
These passive ranging systems include a number of drawbacks including, but not limited to, low signal strength issues, reception of multi-path reflected signals, jamming issues, among others. Accordingly, there is a need for a passive ranging or bi-static radar system which uses GPS pseudolites to overcome any one of or combinations of these issues. There is also a need for using a space-time adaptive processing system in a passive ranging or bi-static radar system to overcome any one of or combinations of these issues.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.
An example of the invention relates to a bi-static radar system. The bi-static radar system comprises a system of positioning signal transmitters transmitting positioning signals, at least one of the positioning system signal transmitters being carried on a pseudolite. The bi-static radar system also comprises a receiving platform, the receiving platform having at least two antennas, a first antenna receiving positioning signals from the positioning signal transmitters, and a second antenna receiving reflected positioning signals from a target.
Another example of the invention relates to a bi-static radar system. The bi-static radar system comprises a constellation of satellites having positioning signal transmitters transmitting positioning signals. The bi-static radar system also comprises a receiving platform, the receiving platform having at least two antennas, a first antenna receiving positioning signals from the positioning signal transmitters, and a second antenna receiving reflected positioning signals from a target. The bi-static radar system further comprises a signal processing system coupled to the at least two antennas, the signal processing system using a spatial or array processing algorithm on the signals received by the second antenna.
Yet another example of the invention relates to a passive ranging system. The passive ranging system comprises a system of positioning signal transmitters transmitting positioning signals, at least one of the positioning system signal transmitters being carried on a pseudolite. The passive ranging system also comprises a receiving platform, the receiving platform having at least two antennas, a first antenna receiving positioning signals from the positioning signal transmitters, and a second antenna receiving reflected positioning signals from a target. The passive ranging system further comprises a signal processing system coupled to the at least two antennas, the signal processing system using space-time adaptive processing (STAP) on the signals received by the second antenna.
Alternative examples and other exemplary embodiments relate to other features and combination of features as may be generally recited in the claims.